Archive for the ‘global positioning’ Category

By Robert Wall and Douglas Barrie
Aviation Week and Space Technology
December 23, 2007

The U.S. military is increasingly interested in developing a new generation of high-speed air-to-surface missiles that could be integrated into stealth aircraft to attack an enemy’s radar sites or fleeting targets.

U.S. Air Force planners are anxious about enhancements in air defense technology, worrying that as powerful computer processing becomes more ubiquitous and network cabling becomes cheaper, adversaries can link radar systems of different types to raise their chances of spotting and potentially shooting down even low-observable aircraft.

Although the military is putting much effort into using directed-energy and network attack tools to thwart such threats, the kinetic kill approach hasn’t fallen out of favor entirely. One reason is that the initial generation of directed-energy systems will still require aircraft to get comparatively close to a threat, while missiles can be launched at greater stand-off ranges. The missiles themselves could also be candidates for directed-energy warheads.

There has been frustration among weapon developers that the U.S. and Europe have not done more to push high-speed technology, with a few exceptions such as the European rocket/ramjet-powered Meteor air-to-air missile. Russia has ramjet-powered air-to-surface weapons in its inventory, and China and India are also pursuing this area aggressively, bemoans a European industry official.

But the situation may be changing. One emerging project, for instance, is a Raytheon initiative to design a ramjet-powered version of the AGM-88 High-Speed Anti-Radiation Missile (HARM), according to a company official. Raytheon has been exploring various options for a ramjet motor, which would be paired with an enhanced HARM front end.

The ramjet concept now undergoing more detailed systems analysis at Raytheon would use an asymmetric intake configuration, with the two ducts on opposite sides of the missile body. The motor would be paired with a standard 10-in.-dia. missile frame, says a European industry official.

In addition to the anti-radar role, the weapon would be aimed to meet the Pentagon’s persistent requirement for higher-speed strike weapons to eliminate time-sensitive targets, which can move quickly and often prove elusive. A HARM coupled with the high-speed motor would likely feature guidance enhancements enabling it to strike coordinates even if a target is not emitting.

Raytheon is working with Diehl Defense to try to interest the German government in the HARM Destruction of Enemy Air Defenses Attack Module (HDAM), an upgrade of the basic weapon which includes an inertial measurement unit/global positioning system for enhanced precision. Germany at one point funded Diehl to develop its own ramjet-powered anti-radar missile, Armiger, but the military ran out of funding.

HARM’s 10-in. diameter would be an integration problem on smaller stealth aircraft, but one U.S. official suggests the effort could be aimed at long-standing U.S. Air Force interest in integrating such a weapon on the B-2 bomber.

The F-22 and F-35 Joint Strike Fighter might potentially be outfitted with reduced-diameter weapons. But they would require much smaller missiles because of the limited space in their internal weapons bays. Even a 7.5-in.-dia. missile could have fit problems because of the inlet ducts and control surfaces, says one industry official who has looked at the problem.

An electronics upgrade slated for the F-22 will give it enhanced ground-emitter location capability, which would significantly boost the aircraft’s capability to destroy enemy air-defenses. But with its current array of air-to-surface weapons, the fighter would have to fly well inside the layered engagement zones of systems such as the Almaz Antey S-400 (SA-21 Growler).

Even though the F-22’s stealth features and ability to fly supersonic without afterburner greatly increase survivability, weaponry with additional stand-off range is seen as important to the fighter’s long-term future. Russia is working on upgrades and follow-on development to the S-400 partly driven by the ability to combat stealth. S-400-derivative systems will also probably begin to proliferate during the coming decade.

One option to deal with this threat would be internal carriage on the F-22 and the F-35 of a 7-in.-dia. version of HARM now being worked on by Raytheon.

However, Alliant Techsystems, which builds the latest upgrade to HARM, the AGM-88E Advanced Anti-Radar Guided Missile (Aargm), also has its eyes on trying to address the emerging market and the internal carriage problem. Aargm has a sophisticated millimeter-wave seeker and an INS/GPS and passive radar detector. The company is exploring various options, including fitting the Aargm front end with an enhanced Amraam air-to-air missile motor. Amraam is smaller than HARM and is a baseline weapon for both the F-35 and F-22, so the integration would not be an issue.

Another option being studied would marry the Aargm seeker with the ramjet-powered Meteor missile. There’s already an agreement with MBDA because of Italian interest in the AGM-88E. The air-to-air Meteor is a candidate weapon for the U.K.’s F-35. Another set of fit check trials were due to be carried out in mid-December on a slightly revised missile configuration to provide adequate clearance in the aircraft’s internal bays.